1. Field of the Invention
The present invention relates generally to slide fasteners, and more particularly to a method of and apparatus for molding a continuous zigzag-shaped strip of thermoplastic coupling elements for use in the production of slide fasteners.
2. Prior Art
Various attempts have been made to produce a continuous zigzag-shaped strip of thermoplastic coupling elements for use in the production of slide fasteners. To this end it has been known to mold the continuous strip on a die wheel having an endless zigzag-shaped pheripheral cavity. The zigzag-shaped cavity includes a plurality of parallel spaced transverse sections and a plurality of longitudinal sections disposed alternately at opposite sides of the cavity and each extending between an adjacent pair of the transverse sections. As the die wheel is continuously rotated, the cavity is advanced such that the transverse sections successively pass a fixed extrusion nozzle to receive heated thermoplastic material extruded from the extrusion nozzle. At that time a predetermined amount of the thermoplastic material is delivered to the individual transverse cavity section from its midportion, and the delivered thermoplastic material-flows rapidly spread to adjacent longitudinal sections and thence into the preceding and succeeding transverse sections. This rapid flow would often cause staggering dimensions of articles (coupling elements) produced, and generation of air cells in the articles.